Wallpaper Calculator

What the wallpaper calculator does

Wallpaper is the one wall material you really cannot afford to underorder, because rolls are made in batches and a later one may not match. This works out how many rolls to buy. You give it the room dimensions and the usable coverage of a roll, and it returns the rolls needed, the wall area, and a cost if you add a price per roll.

It is built around one honest input, the usable coverage, which is what keeps the count realistic. Below is how it works and why that input matters.

How to use it

1. Enter the room length, width, and height, each with its unit.
2. Enter the usable square feet per roll, the coverage you can actually get from a roll, covered in its own section below.
3. Add a price per roll if you want a cost, then press Calculate, or Reset to clear it.

How the roll count is worked out

It works out the wall area as the perimeter of the room times the height, then divides by the coverage of a roll:

Rolls = wall area ÷ usable coverage per roll

The result is rounded up to whole rolls, since you buy them whole. The wall area is the full perimeter times the height, with nothing taken off for doors and windows, which for wallpaper is the right call, as the next section but one explains. The cost, if you add one, is the rolls times your price.

Why it asks for usable coverage

This is the input that matters, and it is worth understanding why it asks for usable coverage rather than the number on the roll. A roll states a total area, but you never get all of it onto the wall. Each strip is trimmed top and bottom to fit the wall height, and the leftover at the end of a roll is rarely a full strip, so some of every roll is offcut.

How much you lose depends on the paper. A plain or random-match paper, with no design to line up, is the most efficient, giving roughly 85 to 90 percent of the roll as usable. So if you are working from a roll's stated coverage, knock it down to a usable figure before entering it, and the rest of this calculation stays honest.

Pattern repeat and dye lots

A patterned paper loses more, and the reason is the repeat. To line the design up across a seam, you often have to shift each new strip down by part of the pattern and cut off the rest, so a paper with a large repeat can waste far more than a plain one, dropping usable coverage well below that 85 to 90 percent. The bigger the repeat, the lower the usable figure you should enter.

The other thing to plan for is the dye lot. Wallpaper is printed in batches, and the colour can shift slightly between them, so rolls from different lots may not match side by side. Buy all your rolls at once from the same lot, and order a little over, both to cover trimming and to keep a spare from that same batch for repairs later.

A worked example: a 12 by 14 room

Say the room is 12 feet by 14 feet with 9 foot ceilings, papered with a plain roll giving about 28 usable square feet.

The walls are 2 × (12 + 14) × 9 = 468 square feet. At 28 usable square feet a roll that is 468 ÷ 28, rounded up to 17 rolls. Most wallpaper is sold in double rolls, around 56 usable square feet each, which would be about 9 of those instead.

Whichever the roll size, entering the usable figure rather than the stated total is what keeps the count from falling short.

Questions people ask

How many rolls of wallpaper do I need?

Work out the wall area, the perimeter times the height, and divide by the usable coverage of a roll. A 12 by 14 room with 9 foot ceilings needs about 17 single rolls, or 9 double rolls.

What is usable coverage?

The part of a roll that actually reaches the wall, after trimming each strip to height and the offcut at the end of the roll. It is less than the total printed on the roll, around 85 to 90 percent for a plain paper and less for a patterned one.

Should I subtract doors and windows?

Not for small ones, which is why the calculator does not. You still hang a full strip and cut around the opening, so the paper is used either way. Only very large openings are worth deducting.

Why buy all the rolls at once?

Because of the dye lot. Colour can vary slightly between print batches, so rolls from different lots may not match. Buy together from one lot and keep a spare.

References

A quick note on the numbers. The wall area is plain geometry, the perimeter times the height. The usable-coverage figures, around 85 to 90 percent for plain paper and less for patterned, and the guidance on pattern repeat and dye lots, follow wallcovering installation practice. The unit conversions follow the US National Institute of Standards and Technology guide.

1. Wallcoverings Association, wallcovering measurement and installation guidance. https://www.wallcoverings.org
2. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811